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A331486 Numbers k which are emirps in more bases 1 < b < k than any previous number.

%I A331486 #17 Jan 25 2020 09:07:55
%S A331486 2,5,7,11,13,17,23,29,31,41,43,53,67,73,79,97,113,127,157,193,223,269,
%T A331486 277,311,379,421,431,467,487,563,613,647,743,907,937,977,1093,1193,
%U A331486 1249,1259,1373,1483,1543,1637,1667,1933,2239,2393,2477,2521,2857,2957,3083
%N A331486 Numbers k which are emirps in more bases 1 < b < k than any previous number.
%C A331486 The corresponding numbers of bases are  0, 1, 3, 6, 8, 9, 12, 13, 17, 21, 24, ... (see the link for more values).
%H A331486 Amiram Eldar, <a href="/A331486/b331486.txt">Table of n, a(n) for n = 1..175</a>
%H A331486 Amiram Eldar, <a href="/A331486/a331486.txt">Table of n, a(n), number of bases for n = 1..175</a>
%e A331486 2 is not emirp in any base.
%e A331486 5 is emirp in one base, 3: 5 is 12 in base 3, and 21 in base 3 is 7 which is also a prime.
%e A331486 7 is emirp in 3 bases, 3, 4, and 5.
%t A331486 emirpQ[n_, b_] := n != (rev = FromDigits[Reverse @ IntegerDigits[n, b], b]) && And @@ PrimeQ[{n, rev}];
%t A331486 emirpCount[n_] := Length @ Select[Range[2, n - 1], emirpQ[n, #] &];
%t A331486 seq = {}; emax = -1; Do[e1 = emirpCount[n]; If[e1 > emax, emax = e1; AppendTo[seq, n]], {n, 2, 3000}]; seq
%Y A331486 Cf. A006567, A080790, A087911, A107129, A228768.
%K A331486 nonn,base
%O A331486 1,1
%A A331486 _Amiram Eldar_, Jan 23 2020